The present invention relates to a golf club shaft and a golf club having the same.
Distributions of flexural rigidity over an entire length from a front end of a golf club shaft up to a grip end have been considered in designing of a golf club in order to increase flight distance of a golf ball. For example, JP H9-234256 A describes designing of such a distribution of the flexural rigidity that it reaches its highest point at a central portion of the shaft between a position 300 mm from a front end of the shaft and a position 300 mm off the grip end of the shaft. Such a distribution of the flexural rigidity maintains the axis of a shaft substantially linearly during a swing and consequently, it is easy to bring back the face surface of a golf club to a position when addressing the ball accurately, thereby an increase of the ball flight distance and improvement of its directionality being achieved.
JP 2002-177423 A describes designing of a change ratio of the flexural rigidity of an area H 100 to 450 mm long in a region 0 to 450 mm from a shaft grip end to 1 to 5 times the change ratio of the flexural rigidity in an area M 200 to 500 mm long in a region 400 to 900 mm from the shaft grip end. According to the same patent document, in the area M, the flexural rigidity is increased gradually from the front end toward the grip end, so that a sufficient flexure and restoration of a deformed shaft induce an increase of the flight distance. In the area H, the change ratio of the flexural rigidity is adjusted to be larger than the area M, and consequently, the flexural rigidity is increased, thereby a firm grip feeling and stability of a flying ball direction being secured.
Additionally, JP 2008-212340 A describes designing so that a difference in flexural rigidity values between a position 150 mm from a front end and a position 950 mm from the front end is 5 kg·m2 or more in a shaft length of 1100 mm or more and the flexural rigidity of a position 150 mm from the front end is 2 kg·m2 or less. This design is made for ordinary amateur golfers whose head speed is relatively slow and is intended to fly a ball high easily to increase the flight distance of a ball.